SEP: A Sustainable Pathway to Terawatt-Scale Solution-Processed Solar Cells from Earth Abundant Elements

NSF可持续能源途径（SEP）计划，在NSF科学，工程和教育可持续性（SEES）倡议的保护伞下，将支持Hugh Hillhouse教授及其同事在华盛顿大学的研究计划，以开发新的太阳能电池技术。可持续能源途径必须产生价格等于或低于不可再生能源的高价值能源产品，具有已知和良性的净环境和社会影响，并且规模足以成为全球能源生产的主要贡献者（太瓦）。基于地壳元素丰度、矿物生产率、矿物原料成本、材料缺陷化学、材料稳定性和可能的p-n结以及光伏发电潜力，Cu 2 ZnSnS 4（CZTS）似乎是太瓦级低成本太阳能收集的最有前途的候选者。在这里，我们将使用严格的生命周期评估（LCA）来分析CZTS太阳能电池的可持续性，并避免困扰其他大规模能源生产路线的间接市场效应。LCA将影响制造器件的合成路线，并有助于引导基础研究的主体集中在：（1）通过应用组合表面处理，最先进的电扫描探针方法，光致发光和从头计算，发展对界面缺陷及其钝化的基本理解;（2）探索在缓冲层中使用新型升压电子掺杂剂俄歇去激发工艺的可能性;（3）开创一种利用石墨烯的独特性质来创建场效应背接触的方法。使用这种3端子背接触架构，将首次调整背表面场。这种额外的自由度将允许表面化学的影响与费米能级平衡分开。可以实现的效率的提高将使该技术达到与当前的非可持续方法在经济上具有竞争力的水平。2009年，国家研究理事会估计，在美国，化石燃料的使用每年造成1200亿美元的非气候损害和20，000人过早死亡。从地球丰富的元素开发低成本太阳能电池的可持续能源途径将对环境和人类健康产生重大影响。此外，太阳能电池市场预计到2017年将达到440亿美元/年，目前，美国公司在薄膜器件的制造和技术开发方面领先于世界。SEP团队所追求的进步可能会将薄膜技术转变为太阳能电池市场的领先地位，并帮助美国公司获得长期的领导地位。该项目还将为这个不断发展的制造业培养一批熟练的科学家和工程师，他们了解可持续工艺的必要性，并欣赏实现这些工艺所需的跨学科协作方法。该项目的影响将通过以下努力扩大：（1）在太平洋科学中心设立一个新的儿童展览，名为“光赛车”，（2）在新的华盛顿大学太阳能试验台设施部署实验性太阳能电池技术;（3）为SunDawg太阳能信息亭配备人员，数千人将在华盛顿大学和西雅图体育赛事中观看该信息亭，（4）增加研究人员在本科研究经验方面已经付出的大量努力（过去十年中与本科生进行了70项长期研究项目）;（5）扩大高中外展计划，在过去两年中，该计划已经导致对西雅图高中的20多次课堂访问，覆盖800多名学生;（6）支持扩大参与的努力，与梅萨外展计划合作，为代表性不足的少数民族提供指导。该项目具有解决关键的基础和技术挑战的变革潜力，这将为薄膜太阳能电池提供新的可持续能源途径，这些薄膜太阳能电池比现有技术具有经济优势，并与利用化石燃料资源竞争。如果成功，该项目可能会将太阳能行业从目前由海外制造的硅太阳能电池主导的行业转变为基于美国制造的铜，锌，锡和硫的新技术。

The NSF Sustainable Energy pathways (SEP) Program, under the umbrella of the NSF Science, Engineering and Education for Sustainability (SEES) initiative, will support the research program of Prof. Hugh Hillhouse and co-workers at the University of Washington to develop new solar cell technology from earth abundant elements. A sustainable energy pathway must yield high-value energy products at or below the price from non-renewables, with a net environmental and societal impact that is known and benign, and at a scale sufficient to become a major contributor to worldwide energy production (terawatts). Based on crustal abundance of the elements, mineral production rates, cost of the mineral feed stocks, the material defect chemistry, stability of the material and likely p-n junctions, and the photovoltaic electricity generation potential, Cu2ZnSnS4 (CZTS) appears to be a most promising candidate for terawatt-scale low-cost solar energy harvesting. Here, we will use a rigorous life cycle assessment (LCA) to analyze the sustainability of CZTS solar cells and avoid indirect market effects that have plagued other large-scale energy production routes. The LCA will affect the synthetic routes to fabricating the devices and help steer a body of fundamental research focusing on: (1) Developing a fundamental understanding of defects at interfaces and their passivation by applying combinatorial surface treatments, state-of-the-art electrical scanning probe methods, photoluminescence, and ab initio calculations; (2) Exploring the possibility of using novel voltage-boosting electron-dopant Auger de-excitation processes in the buffer layer; (3) Pioneering a method to utilize the unique properties of graphene to create a field-effect back contact. Using this 3-terminal back-contact architecture, the back-surface field, for the first time, will be tuned. This extra degree of freedom will allow the effects of surface chemistry to be separated from Fermi level equilibration. The increase in efficiency that could be achieved would bolster this technology to a level that would be economically competitive with current non-sustainable approaches.In 2009 the National Research Council estimated that fossil fuel use accounts for $120B/yr in non-climate damages and 20,000 premature deaths in the U.S. As a result, the development of a sustainable energy pathway to low-cost solar cells from Earth abundant elements will have a substantial impact on the environment and human health. In addition, the solar cell market is predicted to reach $44B/yr by 2017, and currently, U.S. companies lead the world in manufacturing and technology development for thin film devices. Advances such as those being pursued by the SEP team could shift thin film technology into the lead of the solar cell market, and help U.S. companies secure a long-term leadership position. The project will also train a skilled set of scientists and engineers for this growing manufacturing sector who understand the necessity of sustainable processes and appreciate the collaborative interdisciplinary approaches needed to achieve them. The impact of the project will be broadened by efforts including: (1) setting up a new children's exhibit at the Pacific Science Center called Light Racing, (2) deploying experimental solar cell technologies at the new UW Solar Energy Testbed Facility; (3) staffing the SunDawg Solar Kiosk which will be viewed by thousands at University of Washington and Seattle sporting events, (4) increasing the already substantial effort the investigators have in undergraduate research experiences (70 long-term research projects with undergraduates in the last decade); (5) expanding a high-school outreach program that within the past two years has already resulted in greater than 20 classroom visits to Seattle high schools, reaching more than 800 students; and (6) supporting efforts to broaden participation working with the MESA outreach program to provide mentorship to underrepresented minorities. This project has the transformative potential to solve key fundamental and technological challenges that will enable a new sustainable energy pathway for thin film solar cells that have economic advantage over current technology and are competitive with utilizing fossil fuel resources. If successful, the project could transform the solar industry from one currently dominated by silicon solar cells that are manufactured overseas to a new technology based on copper, zinc, tin, and sulfur that are manufactured in the U.S.